Amorphous metal alloy materials have become of interest in recent years due to their unique combination of mechanical, chemical and electrical properties that are especially well-suited for many technical applications. Examples of amorphous metal material properties include the following:
uniform electronic structure, PA1 compositionally variable properties, PA1 high hardness and strength, PA1 flexibility, PA1 soft magnetic and ferroelectric properties, PA1 very high resistance to corrosion and wear, PA1 unusual alloy compositions, and PA1 high resistance to radiation damage.
Of special interest are amorphous alloys having enhanced soft magnetic, ferroelectric and corrosion resistant properties. Such materials would be ideally suited for producing high efficiency powerline transformers and windings for motors.
The unique combination of properties of amorphous metal alloy materials may be attributed to the disordered atomic structure of amorphous materials which ensures that the material is chemically homogeneous and free from the extended defects, such as dislocations and grain boundaries, that are known to limit the performance of crystalline materials. The amorphous state is characterized by a lack of long range periodicity, whereas a characteristic of the crystalline state is its long range periodicity.
Generally, the room temperature stability of amorphous materials depends on various kinetic barriers to the growth of crystal nuclei and to nucleation barriers that hinder the formation of stable crystal nuclei. Such barriers typically are present if the material to be made amorphous is first heated to a molten state, then rapidly quenched or cooled through the crystal nucleation temperature range at a rate that is sufficiently fast to prevent significant nucleation to occur. Such cooling rates are on the order of 10.sup.6 .degree. C./second. Rapid cooling dramatically increases the viscosity of the molten alloy and quickly decreases the length over which atoms can diffuse. This has the effect of preventing crystalline nuclei from forming and yields a metastable, or amorphous, phase.
Processes that provide such cooling rates include sputtering, vacuum evaporation, plasma spraying and direct quenching from the liquid state. It has been found that alloys produced by one method often cannot be similarly produced by another method even though the pathway to formation is in theory the same.
Direct quenching from the liquid state has found the greatest commercial success since a variety of alloys are known that can be manufactured by this technique in various forms such as thin films, ribbons and wires. U.S. Pat. No. 3,856,513 to Chen et al. describes novel metal alloy compositions obtained by direct quenching from the metal and includes a general discussion of this process. Chen et al. describes magnetic amorphous metal alloys formed by subjecting the alloy composition to rapid cooling from a temperature above its melting temperature. A stream of the molten metal is directed into the nip of rotating double rolls maintained at room temperature. The quenched metal, obtained in the form of a ribbon, was substantially amorphous as indicated by x-ray diffraction measurements, was ductile, and had a tensile strength of about 350,000 psi.
U.S. Pat. No. 4,036,638 to Ray et al. describes binary amorphous alloys of iron or cobalt and boron. The claimed amorphous alloys were formed by a vacuum melt-casting process wherein molten alloy was ejected through an orifice and against a rotating cylinder in a partial vacuum of about 100 millitorr. Such amorphous alloys were obtained as continuous ribbons and all exhibited high mechanical hardness and ductility.
The thickness of essentially all amorphous foils and ribbons formed by rapid cooling from the melt are limited by the rate of heat transfer through the material. Generally, the thickness of such films is less than 50 microns. The few materials that can be prepared in this manner include the disclosed by Chen et al. and Ray et al.
Amorphous metal alloy materials prepared by electrodeposition processes have been reported by Lashmore and Weinroth in Plating and Surface Finishing, 72 (August 1982). These materials include Co--P, Ni--P, Co--Re and Co--W compositions. However, the as-formed alloys are inhomogeneous and so can be used in only limited applications.
The above-listed prior art processes for producing amorphous metal alloys depend upon controlling the kinetics of the solidification process; controlling the formation of the alloy from the liquid (molten) state or from the vapor state by rapidly removing heat energy during solidification. Most recently, an amorphous metal alloy composition was synthesized without resort to rapid heat removal. Yeh et al. reported that a metastable crystalline compound Zr.sub.3 Rh, in the form of a thin film, could be transformed into a thin-film, amorphous metal alloy by the controlled introduction of hydrogen gas; Applied Physics Letter 42(3), pp 242-244, Feb. 1, 1983. The amorphous metal alloy had an approximate composition of Zr.sub.3 RhH.sub.5.5.
Yeh et al. specified three requirements as prerequisites for the formation of amorphous alloys by solid state reactions: at least a three component system, a large disparity in the atomic diffusion rates of two of the atomic species, and an absence of a polymorphic crystalline alternative as a final state. Thus, Yeh et al. teaches that solid state reactions would have limited applications for the synthesis of amorphous metal alloy materials.
Sawmer disclosed the formation of amorphous Zr--Co alloys by a solid state reaction in a multilayer configuration, Fifth International Conference on Rapidly Quenched Metals, Wurzburg, Germany, September, 1984. Zirconium and cobalt films, having thicknesses between 100 and 500 Angstroms, are layered together and heat treated at a temperature of about 180.degree. C. A diffusion process formed an amorphous Zr--Co phase at the interface of each adjacent layer.
The known amorphous metal alloys and processes for making such alloys discussed above suffer from the disadvantage that the so-formed amorphous alloy is produced in a limited form, that is, as a thin film such as a ribbon, wire or platelet. These limited shapes place severe restrictions on the applications for which amorphous metal materials may be used.
To produce bulk amorphous metal alloy objects, the formed amorphous alloy must be mechanically reduced to a powder as by chipping, crushing, grinding and ball milling and then recombined in the desire shape. These are difficult processes when it is realized that most amorphous metal alloys have high mechanical strengths and also possess a high degree of hardness.
What is lacking in the area of amorphous metal alloy preparation is a simple process for the direct formation of a large variety of amorphous metal alloys. Especially lacking is a process that would synthesize amorphous metal alloy materials directly as powders suitable for forming bulk amorphous metal alloy shapes.
Hence, it is one object of the present invention to provide novel amorphous metal alloy compositions.
It is another object of the present invention to provide a process for the direct preparation of a large variety of homogeneous amorphous metal alloy compositions.
It is a further object of the present invention to provide a process for the direct preparation of a large variety of homogeneous amorphous metal alloy compositions in a powder form.
It is still another object of the present invention to provide a process for the direct preparation of a large variety of homogeneous amorphous metal alloy powders by solid state reactions.
These and additional objects of the present invention will become apparent in the description of the invention and examples that follow.